If your not trying time your autoattacks perfectly between combat arts, and your using mismatched delay weapons your failing right from the start. Dirge autoattacks are the
metronome for our entire dps output.
In almost every possible scenario an auto attack is gonna do more dps than any combat art or spell you could possibly press.
With this said i find it most common that people push back or delay their autoattacks by chain casting. What i mean is, you only have a certain amount of time before the mob is going to die, in that time you MUST get as many auto attacks off as possible. The timer is ticking as the mobs health is dropping; if it's time for an auto attack and your in the middle of a cast the auto attack waits till the cast is over to trigger and THEN starts to cool down for the next trigger. The farther you delay and push back your auto atacks the less total your dps output will be.
The basic idea is to just autoattack the mob and in between each auto attack add 1 or 2 combat arts/spells. Besides the chain that we're all familiar with, it's almost always gonna hurt you to push more than 2 buttons per auto attack. (depending on weapon delay and haste mod, i'm spoiled with gear so your results may vary)
I recomend using ACT with the previously mentioned plugin to get a feel for your autoatack timing. I've come to realize that alot of players out there who play dirge would benefit in dps from just autoattacking without trying to push buttons, especially if your coming from a background of playing button mashing classes. As with everything else, you need a starting point, and plain auto attacking is as good a place to start as any. Once you've got your auto attacks timed you can add from there. It's alot easier than working it the other way around.
Above all remember your auto attacks are ~70% of your output no matter what your gear is. I can equip the best raid gear with Myth and Marrows or full instance gear or full MC gear: across the board my auto attack stays around 70% of my output.